U.S. patent application number 16/644623 was filed with the patent office on 2021-03-18 for method for preparing catalyst layer, catalyst layer, and membrane-electrode assembly comprising same and fuel cell.
The applicant listed for this patent is LG CHEM, LTD.. Invention is credited to Lee Jin GHIL, Doyoung KIM, Woon Jo KIM.
Application Number | 20210083308 16/644623 |
Document ID | / |
Family ID | 1000005261562 |
Filed Date | 2021-03-18 |
United States Patent
Application |
20210083308 |
Kind Code |
A1 |
GHIL; Lee Jin ; et
al. |
March 18, 2021 |
METHOD FOR PREPARING CATALYST LAYER, CATALYST LAYER, AND
MEMBRANE-ELECTRODE ASSEMBLY COMPRISING SAME AND FUEL CELL
Abstract
The present specification relates to a method for manufacturing
a membrane-electrode assembly, a membrane-electrode assembly
manufactured therefrom, and a fuel cell including the same.
Inventors: |
GHIL; Lee Jin; (Daejeon,
KR) ; KIM; Doyoung; (Daejeon, KR) ; KIM; Woon
Jo; (Daejeon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG CHEM, LTD. |
Seoul |
|
KR |
|
|
Family ID: |
1000005261562 |
Appl. No.: |
16/644623 |
Filed: |
January 17, 2019 |
PCT Filed: |
January 17, 2019 |
PCT NO: |
PCT/KR2019/000697 |
371 Date: |
March 5, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 2008/1095 20130101;
H01M 4/8652 20130101; H01M 4/8892 20130101; H01M 4/8828 20130101;
H01M 4/926 20130101; H01M 8/1004 20130101 |
International
Class: |
H01M 8/1004 20060101
H01M008/1004; H01M 4/88 20060101 H01M004/88; H01M 4/92 20060101
H01M004/92; H01M 4/86 20060101 H01M004/86 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 26, 2018 |
KR |
10-2018-0009860 |
Claims
1. A method for manufacturing a catalyst layer, the method
comprising: preparing a solution that comprises an ionomer and a
solvent, the solvent comprising 2-ethoxyethanol and an
alcohol-based solvent having 1 to 6 carbon atoms; forming a
catalyst slurry composition by adding a carbon powder catalyst to
the solution; and forming a catalyst layer by applying the catalyst
slurry composition onto a base material, and then drying the
catalyst slurry composition, wherein a weight ratio of the carbon
powder catalyst, the alcohol-based solvent having 1 to 6 carbon
atoms, and the 2-ethoxyethanol in the catalyst slurry composition
is from 1:2.5:2.5 to 1:4.5:4.5, and a content of the solvent
comprising the 2-ethoxyethanol and the alcohol-based solvent having
1 to 6 carbon atoms in the catalyst layer is 10 parts by weight to
20 parts by weight based on 100 parts by weight of the catalyst
layer.
2. The method of claim 1, wherein the alcohol-based solvent having
1 to 6 carbon atoms comprises methanol, ethanol, butanol,
1-propanol, isopropanol, or a mixture of two or more thereof.
3. The method of claim 1, wherein the drying is performed at a
temperature of from 30.degree. C. to 40.degree. C. for 30 minutes
or less.
4. The method of claim 1, further comprising, after the forming of
the catalyst slurry composition and before the forming of the
catalyst layer, homogenizing the catalyst slurry composition by
performing sonication on the catalyst slurry composition.
5. The method of claim 1, wherein the ionomer is a fluorine-based
polymer.
6. The method of claim 1, wherein the catalyst layer has a
thickness of 5 .mu.m to 15 .mu.m.
7. A catalyst layer comprising: a carbon powder catalyst; an
ionomer; and a solvent comprising 2-ethoxyethanol and an
alcohol-based solvent having 1 to 6 carbon atoms, wherein a content
of the solvent comprising the 2-ethoxyethanol and the alcohol-based
solvent having 1 to 6 carbon atoms is 10 parts by weight to 20
parts by weight based on 100 parts by weight of the catalyst
layer.
8. A membrane-electrode assembly comprising: an anode catalyst
layer; a cathode catalyst layer; and a polymer electrolyte membrane
between the anode catalyst layer and the cathode catalyst layer,
wherein at least one of the anode catalyst layer and the cathode
catalyst layer comprises the catalyst layer according to claim
7.
9. A fuel cell comprising the membrane-electrode assembly according
to claim 8.
10. The method of claim 1, wherein the alcohol-based solvent having
1 to 6 carbon atoms is 1-propanol.
Description
TECHNICAL FIELD
[0001] This application claims priority to and the benefit of
Korean Patent Application No. 10-2018-0009860 filed in the Korean
Intellectual Property Office on Jan. 26, 2018, the entire contents
of which are incorporated herein by reference.
[0002] The present specification relates to a method for
manufacturing a catalyst layer, a catalyst layer, and a
membrane-electrode assembly and a fuel cell including the same.
BACKGROUND ART
[0003] For a hydrocarbon-based membrane-electrode assembly (MEA),
there is a need for studies on maintaining a constant amount of
solvent in a catalyst electrode in order to assemble an electrolyte
membrane and the catalyst electrode unlike a fluorine-based
membrane-electrode assembly (MEA). The solvent in the catalyst
electrode largely has an advantage in that the solvent in the
catalyst electrode serves to increase a transfer rate to the
electrolyte membrane, and simultaneously, facilitates the control
of occurrence of cracks and dispersion of electrode slurry when the
catalyst electrode is stored for a long period of time and the
electrode slurry is manufactured. However, the solvent in the
catalyst electrode has a problem in that the solvent acts as an
element that hinders the activity of the membrane-electrode
assembly (MEA). The activation (aging) of the membrane-electrode
assembly is largely performed in order to activate the catalyst
electrode, supply water in the membrane-electrode assembly (MEA),
and remove the solvent remaining in the membrane-electrode assembly
(MEA), and in this case, the solvent in the catalyst electrode acts
as a solvent remaining in the membrane-electrode assembly (MEA) to
reduce an activation rate of the membrane-electrode assembly
(MEA).
[0004] Currently, a solvent used most frequently as the solvent in
the electrode is glycerol. In terms of the activity of the
membrane-electrode assembly (MEA), glycerol is not perfectly
removed during the transfer of the membrane-electrode assembly
(MEA) because glycerol has a boiling point of about 290.degree. C.,
and glycerol is slowly removed depending on the flow and reaction
of gas/water during the activation process. In particular, glycerol
has a disadvantage in that it is difficult to remove glycerol due
to a high viscosity thereof. Therefore, a solvent which is easily
removed while acting like glycerol needs to be used in order to
improve the activation rate of the membrane-electrode assembly
(MEA).
DETAILED DESCRIPTION OF INVENTION
Technical Problem
[0005] The present specification has been made in an effort to
provide a method for manufacturing a catalyst layer, a catalyst
layer, and a membrane-electrode assembly and a fuel cell including
the same.
Technical Solution
[0006] An exemplary embodiment of the present specification
provides a method for manufacturing a catalyst layer, the method
including: preparing a solution including: an ionomer; and a
solvent including 2-ethoxyethanol and an alcohol-based solvent
having 1 to 6 carbon atoms; forming a catalyst slurry composition
by adding a carbon powder catalyst to the solution; and forming a
catalyst layer by applying the catalyst slurry composition onto a
base material, and then drying the catalyst slurry composition, in
which a weight ratio of the carbon powder catalyst, the
alcohol-based solvent having 1 to 6 carbon atoms, and the
2-ethoxyethanol in the catalyst slurry composition is 1:2.5:2.5 to
1:4.5:4.5, and a content of the solvent including the
2-ethoxyethanol and the alcohol-based solvent having 1 to 6 carbon
atoms in the catalyst layer is 10 parts by weight to 20 parts by
weight based on 100 parts by weight of the catalyst layer.
[0007] Further, an exemplary embodiment of the present
specification provides a catalyst layer including: a carbon powder
catalyst; an ionomer; and a solvent including 2-ethoxyethanol and
an alcohol-based solvent having 1 to 6 carbon atoms, in which a
content of the solvent including the 2-ethoxyethanol and the
alcohol-based solvent having 1 to 6 carbon atoms is 10 parts by
weight to 20 parts by weight based on 100 parts by weight of the
catalyst layer.
[0008] In addition, an exemplary embodiment of the present
specification provides a membrane-electrode assembly including an
anode catalyst layer, a cathode catalyst layer, and a polymer
electrolyte membrane provided between the anode catalyst layer and
the cathode catalyst layer, in which at least one of the anode
catalyst layer and the cathode catalyst layer includes the
above-described catalyst layer.
[0009] Furthermore, an exemplary embodiment of the present
specification provides a fuel cell including the above-described
membrane-electrode assembly (MEA).
Advantageous Effects
[0010] A method for manufacturing a catalyst layer according to an
exemplary embodiment of the present specification may improve the
dispersibility of an ionomer, and simultaneously, have an excellent
membrane-electrode assembly (MEA) internal activation rate, as
compared to that of a catalyst layer manufactured using glycerol,
by forming a catalyst layer by steps of forming a catalyst slurry
composition to which a solvent including 2-ethoxyethanol is added,
and then re-homogenizing the catalyst slurry composition by
subjecting the catalyst slurry composition to sonication.
[0011] Further, the method for manufacturing a catalyst layer
according to an exemplary embodiment of the present specification
may reduce an ionomer aggregation phenomenon and a crack phenomenon
as compared to the existing manufacturing methods.
[0012] In addition, the method for manufacturing a catalyst layer
according to an exemplary embodiment of the present specification
reduces the permeation of fuel by reducing an ionomer aggregation
phenomenon and a crack phenomenon, so that an open circuit voltage
(OCV) of the fuel cell is improved, thereby improving the
performance of the fuel cell.
BRIEF DESCRIPTION OF DRAWINGS
[0013] FIG. 1 is a view schematically illustrating a structure of a
membrane-electrode assembly.
[0014] FIG. 2 illustrates the performances of electrodes
manufactured by the methods for manufacturing a membrane-electrode
assembly according to Examples 1 and 2 and Comparative Example 1 of
the present specification.
[0015] FIG. 3 illustrates the activation rates of electrodes
manufactured by the methods for manufacturing a membrane-electrode
assembly according to Examples 1 and 2 and Comparative Example 1 of
the present specification.
[0016] 10: Electrolyte membrane [0017] 20: Cathode catalyst layer
[0018] 21: Anode catalyst layer [0019] 40: Cathode gas diffusion
layer [0020] 41: Anode gas diffusion layer [0021] 50: Cathode
[0022] 51: Anode
BEST MODE
[0023] Hereinafter, the present specification will be described in
more detail.
[0024] In the present specification, "on" means not only being
disposed while being physically brought into contact with one
layer, but also being disposed on the one layer in position. That
is, a layer disposed on any one layer may also have another layer
therebetween.
[0025] When one part "includes" one constituent element in the
present specification, unless otherwise specifically described,
this does not mean that another constituent element is excluded,
but means that another constituent element may be further
included.
[0026] An exemplary embodiment of the present specification
provides a method for manufacturing a catalyst layer, the method
including: preparing a solution including: an ionomer; and a
solvent including 2-ethoxyethanol and an alcohol-based solvent
having 1 to 6 carbon atoms; forming a catalyst slurry composition
by adding a carbon powder catalyst to the solution; and forming a
catalyst layer by applying the catalyst slurry composition onto a
base material, and then drying the catalyst slurry composition, in
which a weight ratio of the carbon powder catalyst, the
alcohol-based solvent having 1 to 6 carbon atoms, and the
2-ethoxyethanol in the catalyst slurry composition is 1:2.5:2.5 to
1:4.5:4.5, and a content of the solvent including the
2-ethoxyethanol and the alcohol-based solvent having 1 to 6 carbon
atoms in the catalyst layer is 10 parts by weight to 20 parts by
weight based on 100 parts by weight of the catalyst layer.
[0027] When a catalyst layer is manufactured by using the solvent
including 2-ethoxyethanol, 2-ethoxyethanol has a boiling point of
135.degree. C., so that a drying process is performed at a lower
temperature and a shorter drying time than the case where a solvent
having a higher boiling point than 135.degree. C., which is used in
the related art, for example, a solvent such as glycerol (boiling
point: 290.degree. C.) is used. Accordingly, in a transfer process
of a membrane-electrode assembly (MEA) including the catalyst
layer, it is possible to obtain a similar transfer rate and a
similar performance while having an improved activation rate.
[0028] In an exemplary embodiment of the present specification, the
solution may include: an ionomer; and a solvent including
2-ethoxyethanol and an alcohol-based solvent having 1 to 6 carbon
atoms.
[0029] In the present specification, as the carbon powder catalyst,
it is possible to use a catalyst in which a metal is carried on the
surface of a carbon powder.
[0030] In the present specification, as the carbon powder catalyst,
it is possible to use a catalyst (Pt/C) in which platinum is
carried on the surface of a carbon powder.
[0031] As the carbon powder, it is possible to use one or a mixture
of two or more selected from the group consisting of graphite,
carbon black, acetylene black, Denka black, Ketjen black, activated
carbon, mesoporous carbon, carbon nanotube, carbon nano fiber,
carbon nano horn, carbon nano ring, carbon nano wire, fullerene
(C60), and Super P, but the carbon powder is not limited
thereto.
[0032] In the carbon powder catalyst (Pt/C) in which platinum is
carried, an amount of platinum carried based on carbon is
preferably 10 parts by weight to 80 parts by weight, and more
preferably 30 parts by weight to 70 parts by weight, based on 100
parts by weight of carbon, but is not limited thereto.
[0033] When the amount of platinum carried based on carbon is more
than 80 parts by weight, there may occur a problem in that the
thickness of the electrode in the membrane-electrode assembly
becomes thinner. When the thickness of the electrode becomes
thinner, the probability that hydrogen and oxygen gases directly
reach the membrane without being oxidized/reduced in the electrode
layer is increased, so that there may occur a problem in that the
entire performance of the membrane-electrode assembly is reduced,
and the durability deteriorates.
[0034] In an exemplary embodiment of the present specification, the
ionomer is a fluorine-based polymer.
[0035] Specifically, the ionomer may serve to provide a channel
through which ions produced by reaction between fuel such as
hydrogen or methanol and a catalyst move to an electrolyte
membrane.
[0036] In the present specification, the ionomer may be a
perfluorosulfonic acid (PFSA)-based polymer or a
perfluorocarboxylic acid (PFCA)-based polymer. As the
perfluorosulfonic acid-based polymer and the perfluorocarboxylic
acid-based polymer, Nafion (manufactured by Dupont Co., Ltd.) and
Flemion (manufactured by Asahi Glass Co., Ltd.) may be used,
respectively.
[0037] According to an exemplary embodiment of the present
specification, the ionomer may have a weight average molecular
weight of 240 g/mol to 200,000 g/mol, and specifically 240 g/mol to
10,000 g/mol.
[0038] In the present specification, a content of the ionomer is
preferably 5 parts by weight to 150 parts by weight based on 100
parts by weight of the carbon powder catalyst, but is not limited
thereto.
[0039] When the content of the ionomer is less than 5 parts by
weight based on the carbon powder catalyst, ions are not properly
transferred to the electrolyte membrane, and when the content of
the ionomer is more than 150 parts by weight based on the carbon
powder catalyst, the ionomer blocks the permeation of gas, thereby
degrading the performance of the membrane-electrode assembly.
[0040] In an exemplary embodiment of the present specification, the
alcohol-based solvent having 1 to 6 carbon atoms is a solvent that
may disperse the catalyst, and it is preferred that a solvent which
can be evaporated within a range of 30.degree. C. to 100.degree. C.
is used. Accordingly, water or an alcohol-based solvent such as
methanol, ethanol, and propanol is suitable.
[0041] When a solvent having a high volatilization temperature, for
example, a solvent which can be evaporated at a temperature more
than 100.degree. C. is used as the alcohol-based solvent having 1
to 6 carbon atoms, during the manufacture of an electrode, the
density of the electrode becomes compact, so that it is difficult
to form pores, thereby affecting the degradation in
performance.
[0042] Further, since 2-ethoxyethanol is used for assembling the
membrane-electrode assembly (MEA) and maintaining the remaining
solvent, it is not suitable for 2-ethoxyethanol to be used as the
alcohol-based solvent having 1 to 6 carbon atoms. In addition,
since 2-ethoxyethanol has a boiling point of 135.degree. C., which
is out of a temperature range suitable for the alcohol-based
solvent having 1 to 6 carbon atoms, it is not suitable for
2-ethoxyethanol to be used as the alcohol-based solvent having 1 to
6 carbon atoms.
[0043] The alcohol-based solvent having 1 to 6 carbon atoms may be
one or two or more selected from the group consisting of water,
methanol, ethanol, butanol, 1-propanol, and isopropanol.
Preferably, the alcohol-based solvent having 1 to 6 carbon atoms
may be water or 1-propanol, but is not limited thereto.
[0044] In an exemplary embodiment of the present specification, the
alcohol-based solvent having 1 to 6 carbon atoms is water.
[0045] In an exemplary embodiment of the present specification, the
alcohol-based solvent having 1 to 6 carbon atoms is 1-propanol.
[0046] In an exemplary embodiment of the present specification, the
alcohol-based solvent having 1 to 6 carbon atoms is water and
1-propanol.
[0047] In the present specification, a content of the alcohol-based
solvent having 1 to 6 carbon atoms is preferably 5 parts by weight
to 99 parts by weight based on 100 parts by weight of the entire
catalyst slurry composition, but is not limited thereto.
Specifically, the content may be 5 parts by weight to 30 parts by
weight, preferably 10 parts by weight to 20 parts by weight.
[0048] In an exemplary embodiment of the present specification, the
solvent including 2-ethoxyethanol and the alcohol-based solvent
having 1 to 6 carbon atoms may be composed of 2-ethoxyethanol and
an alcohol-based solvent having 1 to 6 carbon atoms.
[0049] When the solvent including 2-ethoxyethanol and the
alcohol-based solvent having 1 to 6 carbon atoms is composed of
2-ethoxyethanol and an alcohol-based solvent having 1 to 6 carbon
atoms, 2-ethoxyethanol and the alcohol-based solvent having 1 to 6
carbon atoms may satisfy a weight ratio of 1:1 to 2:1, preferably a
weight ratio of 2:1. When 2-ethoxyethanol and the alcohol-based
solvent having 1 to 6 carbon atoms satisfy a weight ratio of 2:1,
the drying time is easily controlled while maintaining the
dispersibility of the catalyst.
[0050] In an exemplary embodiment of the present specification,
when the solvent including 2-ethoxyethanol and the alcohol-based
solvent having 1 to 6 carbon atoms is composed of 2-ethoxyethanol
and an alcohol-based having 1 to 6 carbon atoms, a content of the
2-ethoxyethanol is preferably 30 parts by weight to 70 parts by
weight based on 100 parts by weight of the catalyst slurry
composition, but is not limited thereto.
[0051] In an exemplary embodiment of the present specification, a
weight ratio of a carbon catalyst powder, an alcohol-based solvent
having 1 to 6 carbon atoms, and 2-ethoxyethanol in the catalyst
slurry composition may satisfy 1:2.5:2.5 to 1:4.5:4.5.
[0052] In another exemplary embodiment of the present
specification, a weight ratio of a carbon catalyst powder, an
alcohol-based solvent having 1 to 6 carbon atoms, and
2-ethoxyethanol in the catalyst slurry composition may satisfy
1:3:3 to 1:4:4.
[0053] In the catalyst slurry composition, when the content of
2-ethoxyethanol is more than a range of the above-described weight
ratio of the carbon catalyst powder, the alcohol-based solvent
having 1 to 6 carbon atoms, and 2-ethoxyethanol, the catalyst
slurry composition is in a precipitate state, so that a stable
dispersion state cannot be achieved. Furthermore, when the content
of 2-ethoxyethanol is less than a range of the above-described
weight ratio of the carbon catalyst powder, the alcohol-based
solvent having 1 to 6 carbon atoms, and 2-ethoxyethanol, the amount
of solvent remaining in the drying process after the manufacture of
the electrode is insufficient, so that there may occur a problem in
that the electrode is not effectively transferred to one surface or
both surfaces of the electrolyte membrane.
[0054] In the present specification, the remaining solvent means
all the remaining solvents in a catalyst layer manufactured by the
method for manufacturing a catalyst layer, and an amount of solvent
remaining (%) means at what percentage the weight of all the
solvents included in the catalyst layer is included based on 100
parts by weight of the catalyst layer.
[0055] In an exemplary embodiment of the present specification, a
content of the solvent including 2-ethoxyethanol and the
alcohol-based solvent having 1 to 6 carbon atoms, which is included
in the catalyst layer, may be 10 parts by weight to 20 parts by
weight, preferably 10 parts by weight to 15 parts by weight, based
on 100 parts by weight of the catalyst layer.
[0056] When the content of the solvent including 2-ethoxyethanol
and the alcohol-based solvent having 1 to 6 carbon atoms in the
catalyst layer is more than 20 parts by weight based on 100 parts
by weight of the catalyst layer, the solvent is suddenly
volatilized during the transfer of the catalyst layer to the
electrolyte membrane, so that a gas trap phenomenon breaking the
electrode structure may occur.
[0057] When the content of the solvent including 2-ethoxyethanol
and the alcohol-based solvent having 1 to 6 carbon atoms in the
catalyst layer is less than 10 parts by weight based on 100 parts
by weight of the catalyst layer, the amount of solvent remaining is
insufficient, so that there may occur a problem in that the
electrode is not effectively transferred to one surface or both
surfaces of the electrolyte membrane.
[0058] In the forming of the catalyst layer by applying the
catalyst slurry composition of the present specification onto a
base material, and then drying the catalyst slurry composition, the
drying may be performed within a range of 30.degree. C. to
40.degree. C. for 30 minutes or less.
[0059] Through the drying process performed within the range of
30.degree. C. to 40.degree. C. for 30 minutes or less, the content
of the solvent including 2-ethoxyethanol and the alcohol-based
solvent having 1 to 6 carbon atoms in the catalyst layer may be
adjusted within a range of 10 parts by weight to 20 parts by weight
based on 100 parts by weight of the catalyst layer.
[0060] FIG. 2 illustrates a result in which a case of a fuel cell
manufactured by using 2-ethoxyethanol for assembling the
membrane-electrode assembly (MEA) and maintaining the remaining
solvent (Examples 1 and 2) exhibits a similar performance as
compared to a case of a fuel cell manufactured by using glycerol
(Comparative Example 1).
[0061] Further, FIG. 3 illustrates that in the case of a
membrane-electrode assembly (MEA) manufactured by using
2-ethoxyethanol for assembling the membrane-electrode assembly
(MEA) and maintaining the remaining solvent (Examples 1 and 2), the
activation rate and the saturation rate are improved as compared to
the case of a membrane-electrode assembly (MEA) manufactured by
using glycerol (Comparative Example 1).
[0062] In an exemplary embodiment of the present specification,
homogenizing the catalyst slurry composition, which is formed
through the forming of the catalyst slurry composition by adding
the carbon powder catalyst to the solution, by subjecting the
catalyst slurry composition to sonication may be performed.
[0063] In the present specification, the sonication may be composed
of a tip type or a bath type.
[0064] In the present specification, the sonication means a
behavior that disperses particles by adding energy having a
frequency of 20 kHz or more to the particles, energy having a
relatively low and constant size is used in the bath type, and in
the tip type, high energy amounting to about 50 times that of the
bath type may be variably added.
[0065] In general, ionomers are aggregated with one another in the
solvent by electrostatic attractive force and thus present as an
aggregate having a particle diameter of 0.01 .mu.m to 1 .mu.m, and
a unit particle formed by the aggregation of the ionomers in the
solvent is referred to as an ionomer cluster. When the ionomer
clusters are dispersed through sonication, specifically, the tip
type or bath type sonication, most of the ionomer clusters are
uniformly dispersed so as to have an average particle diameter of
10 nm to 500 nm, preferably 10 nm to 300 nm.
[0066] The tip type sonication may be performed for 10 minutes to
30 minutes, but the time is not limited thereto. The bath type
sonication may be performed for 20 minutes to 120 minutes,
preferably 30 minutes to 60 minutes.
[0067] When the sonication is performed within the above time
range, it is possible to prevent the occurrence of a topical
ionomer aggregation phenomenon. When the sonication is performed
more than the above time range, the dispersion effect as compared
to time is not significant, so that the sonication may be
inefficient.
[0068] In order to form a catalyst layer having a uniform
structure, a sufficient absorption strength between the ionomer and
a carbon support in the catalyst is important, and when a particle
diameter of the ionomer is adjusted to be small through the
sonication, the ionomer may be uniformly absorbed onto the carbon
support in the catalyst.
[0069] In an exemplary embodiment of the present specification, a
catalyst slurry composition in the form where the catalyst and the
ionomer are dispersed in the solution maintains a precipitate
state, so that in order for the catalyst slurry composition to be
able to maintain a stable dispersion state, the method includes
additionally performing the stirring of the catalyst slurry
composition before the sonication step.
[0070] When the catalyst slurry composition is in a precipitate
state and thus fails to achieve a stable dispersion state, the
amount of catalyst dispersed varies, so that differences in amount
of catalyst and dispersity of the catalyst at each portion occur,
and the viscosity is randomly increased by aggregation of particles
settling down on the bottom, so that it is difficult to obtain
constant physical properties, but through the stirring step, the
dispersity of catalyst particles is relatively narrowed, so that it
is possible to prevent an aggregation phenomenon of particles and
uniformly maintain the dispersion state of the catalyst slurry.
[0071] In an exemplary embodiment of the present specification,
forming a catalyst layer by applying the catalyst slurry
composition, which is subjected to the homogenizing of the catalyst
slurry composition by subjecting the catalyst slurry composition to
the sonication, onto a base material, and then drying the catalyst
slurry composition is performed.
[0072] The base material is not particularly limited, but may be a
fluorine-based film. Specifically, the base material may be
selected from a polytetrafluoroethylene (PTFE) film, a polyethylene
terephthalate (PET) film, a polyethylene naphthalate (PEN) film,
and a polyimide (PI) film.
[0073] In an exemplary embodiment of the present specification, the
application may be performed by one method selected from the group
consisting of a spray coating method, a screen printing method, a
tape casting method, a brushing method, a slot die casting method,
a bar-casting method, and ink jetting.
[0074] In an exemplary embodiment of the present specification, the
catalyst layer has a thickness of 5 .mu.m to 15 .mu.m.
[0075] An exemplary embodiment of the present specification
provides a catalyst layer including: a carbon powder catalyst; an
ionomer; and a solvent including 2-ethoxyethanol, in which a
content of the solvent including 2-ethoxyethanol is 10 parts by
weight to 20 parts by weight based on 100 parts by weight of the
carbon powder catalyst in the catalyst layer.
[0076] The definitions of the carbon powder catalyst, the ionomer,
and the solvent including 2-ethoxyethanol included in the catalyst
layer are the same as those described above.
[0077] In addition, an exemplary embodiment of the present
specification provides a membrane-electrode assembly including an
anode catalyst layer, a cathode catalyst layer, and a polymer
electrolyte membrane provided between the anode catalyst layer and
the cathode catalyst layer, in which at least one of the anode
catalyst layer and the cathode catalyst layer includes the catalyst
layer.
[0078] The membrane-electrode assembly may further include a
cathode gas diffusion layer provided on a surface opposite to a
surface of the cathode catalyst layer on which the electrolyte
membrane is provided and an anode gas diffusion layer provided on a
surface opposite to a surface of the anode catalyst layer on which
the electrolyte membrane is provided.
[0079] The anode gas diffusion layer and the cathode gas diffusion
layer are each provided on a surface of the catalyst layer, serve
as a current conductor and a channel through which a reaction gas
and water move, and have a porous structure.
[0080] The gas diffusion layer is not particularly limited as long
as the gas diffusion layer is generally a conductive base material
having conductivity and a porosity of 80% or more, and may include
a conductive base material selected from the group consisting of
carbon paper, carbon cloth, and carbon felt. The conductive base
material may have a thickness of 30 .mu.m to 500 .mu.m. When the
thickness is a value within the above range, the balance between
mechanical strength and diffusivity of gas and water may be
appropriately controlled. The gas diffusion layer may be formed by
further including a micropore layer formed on one surface of the
conductive base material, and the micropore layer may be formed by
including a carbon-based material and a fluorine-based resin. The
micropore layer may suppress the occurrence of a flooding
phenomenon by promoting the discharge of excessive moisture present
in the catalyst layer.
[0081] As the carbon-based material, it is possible to use one or a
mixture of two or more selected from the group consisting of
graphite, carbon black, acetylene black, Denka black, Ketjen black,
activated carbon, mesoporous carbon, carbon nanotube, carbon nano
fiber, carbon nano horn, carbon nano ring, carbon nano wire,
fullerene (C60), and Super P, but the carbon-based material is not
limited thereto.
[0082] As the fluorine-based resin, it is possible to use one or a
mixture of two or more selected from the group consisting of
polytetrafluoroethylene, polyvinylidene fluoride (PVdF), polyvinyl
alcohol, cellulose acetate, a copolymer of polyvinylidene
fluoride-hexafluoropropylene (PVdF-HFP), and a styrene-butadiene
rubber (SBR), but the fluorine-based resin is not limited
thereto.
[0083] As a method of forming a catalyst layer by using the
catalyst slurry composition, a typical method known in the art may
be used, and for example, the catalyst layer may be formed by
applying and drying the catalyst slurry composition onto the gas
diffusion layer. In this case, a plurality of catalyst layers may
also be formed by sequentially applying and drying catalyst slurry
compositions having different contents of an ionomer.
[0084] In this case, examples of a method of applying the catalyst
composition onto a gas diffusion layer include a method such as
printing, tape casting, slot die casting, spray, rolling, blade
coating, spin coating, inkjet coating, or brushing, but are not
limited thereto. Preferably, the catalyst layer may be manufactured
as a reinforced membrane by forming a membrane by a casting method
using the catalyst slurry composition, or impregnating an ion
conductive polymer into pores in a porous support.
[0085] The gas diffusion layer may have an average thickness of 200
.mu.m to 500 .mu.m. In this case, there is an advantage in that an
optimum state is achieved from the viewpoint of minimizing the
reactant gas transfer resistance through the gas diffusion layer
and containing a suitable moisture in the gas diffusion layer.
[0086] FIG. 1 is a view schematically illustrating a structure of a
membrane-electrode assembly, and the membrane-electrode assembly
may include an electrolyte membrane 10, and a cathode 50 and an
anode 51 positioned to face each other with the electrolyte
membrane 10 interposed therebetween. Specifically, the cathode may
include a cathode catalyst layer 20 and a cathode gas diffusion
layer 40 which are provided sequentially from the electrolyte
membrane 10, and the anode may include an anode catalyst layer 21
and an anode gas diffusion layer 41 which are provided sequentially
from the electrolyte membrane 10.
[0087] Further, an exemplary embodiment of the present
specification provides a fuel cell including the above-described
membrane-electrode assembly.
MODE FOR INVENTION
[0088] Hereinafter, the present specification will be described in
detail with reference to Examples for specifically describing the
present specification. However, the Examples according to the
present specification may be modified in various forms, and it is
not interpreted that the scope of the present specification is
limited to the Examples to be described below. The Examples of the
present specification are provided to more completely explain the
present specification to a person with ordinary skill in the
art.
EXAMPLES
Example 1
[0089] 3M 825 ionomer was added to a solution in which 1-propanol
and 2-ethoxyethanol were mixed at a weight ratio of 3:4.
Thereafter, a catalyst slurry composition was manufactured by
adding a TEC 10V50E carbon powder catalyst sold by Tanaka Kikinzoku
Kogyo K.K. thereto so as for a weight ratio of the ionomer and the
carbon powder catalyst to be 0.66:1. In this case, in the catalyst
slurry composition, a weight ratio of the carbon powder
catalyst:1-propanol:2-ethoxyethanol was 1:3:4. After the catalyst
slurry composition was stirred at room temperature for 1 hour by
using a magnetic stirrer, and then dispersed at room temperature
for 1 hour by using a bath type ultrasonic dispersion machine, the
temperature was decreased to a state of 50.degree. C. or less, and
the catalyst slurry composition was dispersed for 15 minutes by
using a tip type ultrasonic dispersion machine. After a catalyst
layer was cast onto a PTFE film with a doctor blade on a horizontal
plate of an applicator in a clean bench by using the catalyst
slurry composition, a catalyst layer was finally manufactured by
drying the cast catalyst layer at 35.degree. C. for 30 minutes.
Example 2
[0090] A catalyst layer was manufactured in the same manner as in
Example 1, except that the carbon powder catalyst, 1-propanol, and
2-ethoxyethanol were mixed at a weight ratio of 1:3:3.
Comparative Example 1
[0091] A catalyst slurry composition was manufactured in the same
manner as in Example 1, except that glycerol was used instead of
2-ethoxyethanol, and the carbon powder catalyst, 1-propanol, and
glycerol were mixed at a weight ratio of 1:6.4:0.5. After a
catalyst layer was cast onto a PTFE film with a doctor blade on a
horizontal plate of an applicator in a clean bench by using the
manufactured catalyst slurry composition, a catalyst layer was
finally manufactured by drying the cast catalyst layer at
35.degree. C. for 30 minutes and at 140.degree. C. for 30
minutes.
Comparative Example 2
[0092] A catalyst layer was manufactured in the same manner as in
Example 2, except that an electrode catalyst layer was cast onto a
PTFE film, and then dried at 35.degree. C. for 45 minutes.
Comparative Example 3
[0093] An electrode was manufactured in the same manner as in
Example 1, except that the carbon powder catalyst, 1-propanol, and
2-ethoxyethanol were mixed at a weight ratio of 1:1:5.
[0094] In order to confirm the amount of solvent remaining (%), the
remaining solvent was completely removed by measuring the weight of
the manufactured electrode, and then drying the electrode in an
oven at 140.degree. C. overnight. Thereafter, the electrode was
removed from a base material, and then the weight of the base
material was measured. The amount of solvent remaining (%) could be
ascertained by the following Equation 1.
Amount of solvent remaining ( % ) = ( Weight of electrode before
being dried overnight - Weight of electrode after being dried
overnight ) Weight of electrode before being dried overnight -
Weight of base material .times. 100 [ Equation 1 ] ##EQU00001##
[0095] The transfer states and amounts of solvent remaining (%) of
the catalyst layers according to Examples 1 and 2 and Comparative
Examples 1 to 3 are shown in the following Table 1.
TABLE-US-00001 Amount of 2-ethoxy catalyst I-PA Glycerol Ionomer
ethanol Amount (weight (weight (weight (weight (weight of solvent
ratio) ratio) ratio) ratio) ratio) Drying condition remaining
Result Example 1 1 3 1.65 4 35.degree. C. 30 min 16% Good transfer
Example 2 1 3 1.65 3 35.degree. C. 30 min 14% Good transfer
Comparative 1 6.4 0.5 1.65 35.degree. C. 30 min, 9% Good transfer
Example 1 140.degree. C. 30 min Comparative 1 3 1.65 3 35.degree.
C. 45 min 6% Poor transfer Example 2 Comparative 1 1 1.65 5
Dispersion of Example 3 catalyst slurry .chi.
[0096] As could be seen in Table 1, since the catalyst layer
manufactured by the method for manufacturing a catalyst layer
according to the present specification satisfied a specific weight
ratio of the carbon powder catalyst, 1-propanol, and
2-ethoxyethanol, the catalyst layer could be stably manufactured by
adjusting the amount of solvent remaining to 10% to 20% with a
drying time less than that in Comparative Example 1 in which
glycerol was used instead of 2-ethoxyethanol.
[0097] The catalyst layer in Comparative Example 2 in which the
amount of solvent remaining was 5% was not effectively transferred
to one surface of the electrolyte membrane, and in the case of
Comparative Example 3 in which the weight ratio of the carbon
powder catalyst, the alcohol-based solvent having 1 to 6 carbon
atoms, and 2-ethoxyethanol in the catalyst slurry composition did
not satisfy 1:2.5:2.5 to 1:4.5:4.5, the catalyst slurry composition
was in a precipitate state and thus failed to achieve a stable
dispersion state.
Experimental Example 1
[0098] The membrane-electrode assemblies (MEA) to which the
electrode catalyst layer in Examples 1 and 2 and Comparative
Example 1 were applied were evaluated. A sPEEK-based
hydrocarbon-based polymer membrane was used as the electrolyte
membrane, 10BB manufactured by SGL Carbon Group was used as a gas
diffusion layer (GDL), and a membrane-electrode assembly having a
thickness within a range of 380 .mu.m to 420 .mu.m was used. A
compression ratio of the GDL was set to 25%, and a glass fiber
sheet was used in order to maintain the compression ratio. A unit
battery cell was evaluated by manufacturing a membrane-electrode
assembly having an active area of 25 cm.sup.2. The unit battery
cell was evaluated by using the electrodes in the same example in
the anode and the cathode. A PEMFC station device manufactured by
Scribner Associates Inc. was used as an evaluation device, the
performance was evaluated by maintaining the temperature of the
cell at 70.degree. C. and maintaining the humidity condition at RH
50%, and the results thereof are illustrated in FIG. 2.
[0099] According to FIG. 2, it can be seen that the electrodes
manufactured by the method for manufacturing a membrane-electrode
assembly (MEA) according to the present specification (Examples 1
and 2) have little difference in performance from Comparative
Example 1 in which glycerol was used instead of
2-ethoxyethanol.
Experimental Example 2
[0100] The activation rates of the membrane-electrode assemblies
(MEA) to which the electrode catalyst layers in Examples 1 and 2
and Comparative Example 1 were applied were measured and evaluated
at an interval of 5 minutes at 0.6 v and at an interval of 10
seconds at 0.3 V. A sPEEK-based hydrocarbon-based polymer membrane
was used as the electrolyte membrane, 10BB manufactured by SGL
Carbon Group was used as a gas diffusion layer (GDL), and a
membrane-electrode assembly having a thickness within a range of
380 .mu.m to 420 .mu.m was used. A compression ratio of the GDL was
set to 25%, and a glass fiber sheet was used in order to maintain
the compression ratio. An activation rate was evaluated by
manufacturing a membrane-electrode assembly having an active area
of 25 cm.sup.2. The activation rate was evaluated by using the
electrodes in the same example in the anode and the cathode. A
PEMFC station device manufactured by Scribner Associates Inc. was
used as an evaluation device, the activation rate was evaluated by
maintaining the temperature of the cell at 70.degree. C. and
maintaining the humidity condition at RH 100%, and the results
thereof are illustrated in FIG. 3.
[0101] According to FIG. 3, it can be seen that the electrodes
manufactured by the method for manufacturing a membrane-electrode
assembly (MEA) according to the present specification (Examples 1
and 2) have a higher initial activation rate and a significantly
higher saturation rate than those of Comparative Example 1 in which
glycerol was used instead of 2-ethoxyethanol.
* * * * *